<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  <title>CSS控制表单样式</title>
  <link href="style25.css" type="text/css" rel="stylesheet" />
</head>
<body>
  <form action="#" method="post">
    <p>
      <span>账号：</span>
      <input type="text" name="username" class="num" pattern="^[a-zA-Z][a-zA-Z0-9_]{4,15}$" />
    </p>
    <p>
      <span>密码：</span>
      <input type="password" name="pwd" class="pass" pattern="^[a-zA-Z]\w{5,17}$" />
    </p>
    <p>
      <input type="button" class="btn01" value="登录" />
    </p>
  </form>
</body>
</html>